Genetically transmitted retroviruses have been isolated from five different primate species. These include: type C viruses from two Old World monkeys (baboon and rhesus) and from a New World primate (owl monkey); and type D viruses from Old World (langur) and New World (squirrel monkey) primates. Endogenous viro-genes related to each of these viruses can be detected in these and related species, are present in multiple copies, and evolve as cellular genes. Using somatic cell hybridization, immunological, and nucleic acid hybridization techniques, a new gene, Bevi, on human chromosome six was shown to be a preferred integration site for baboon type C proviral DNA. The feline oncornavirus-associated cell membrane antigen (FOCMA) was shown to be encoded by the feline sarcoma virus (FeSV) genome. A polyprotein of 85,000 M.W. containing "gag" gene (p15 and p12) and FOCMA antigenic determinants has been isolated from pseudotype virions, providing an approach to purifying a protein which can immunize cats against tumors induced by feline type C viruses.